CN112349907B - Composite binder material and preparation method and application thereof - Google Patents

Abstract

The present invention belongs to the technical field of lithium-ion batteries, and specifically relates to a composite binder material and a preparation method and use thereof. The present invention can improve the cycle stability of silicon-based negative electrodes, and at the same time improve the first coulomb efficiency of silicon-based negative electrodes. Through the nucleophilic reaction of aniline on polyvinyl pyrrolidone, a PANI-PVP binder with electrical conductivity is polymerized. The good bonding and toughness of PVP in the binder reduce the volume expansion effect of the active material and improve the stability of the electrode; the good electronic conductivity of PANI bridges the cracks generated during the cycle, ensures the electrical contact of the electrodes, reduces the capacity loss of the silicon-based negative electrode during the cycle, and improves the cycle performance. At the same time, when compounded with carbon nanotubes, the carbon nanotubes not only act as a conductive additive to improve electronic conductivity, but also further act as a reinforcing agent to greatly improve the mechanical properties and bonding strength of the binder.

Description

A composite binder material and its preparation method and use

Technical Field

The invention belongs to the technical field of lithium ion batteries, and in particular relates to a composite binder material and a preparation method and application thereof.

Background technique

In recent years, with the increasing popularity of new energy vehicles and the rapid development of electronic devices such as laptops and smart phones, the development and progress of lithium-ion battery technology, as the core of energy supply, has been driven. At the same time, it has also put forward higher and higher requirements for lithium-ion batteries, such as higher energy density, faster charging and discharging speeds, better endurance and a more relaxed usage environment.

In order to develop high-energy-density rechargeable lithium-ion batteries, adding silicon materials with a theoretical gram capacity of up to 4200mAh/g to the negative electrode is currently the main research direction. However, due to the large volume effect during the process of lithium extraction, the silicon particles are pulverized and lose electrical contact with the conductive agent, which destroys the entire electrode structure, resulting in capacity decay and poor cycle performance. The binder system suitable for silicon negative electrodes is an important direction for solving the problem of silicon negative electrode cycling. The silicon negative electrode binders reported in the literature include PAA, CMC/SBR, sodium alginate, chitosan, PI, and PAI, but these binders do not have the ability to conduct electrons or have low bonding strength, and cannot take into account both electrode structure stability and electronic conductivity. Therefore, it is urgent to develop a negative electrode binder suitable for silicon-based negative electrodes.

Among them, the use of the existing PVP-PANI-based conductive polymer binder achieves the cycle performance and good rate performance of the silicon negative electrode at room temperature or high temperature. However, the study found that the polymer binder has the problem of not being able to balance the cycle performance and rate performance during use. The cycle performance is good but the rate low temperature performance is often reduced. This is because the higher the proportion of PANI in the polymer, the higher the conductivity of the binder, but the mechanical strength will decrease, resulting in the loss of active lithium during long-term cycles.

Summary of the invention

The purpose of the present invention is to improve the defects of the prior art and provide a carbon nanotube-enhanced conductive polymer composite binder and a preparation method and application thereof. The addition of carbon nanotubes to the conductive polymer can enhance the mechanical strength of the composite binder and reduce the bulk resistance effect of the composite binder. The composite binder can simultaneously improve the cycle performance, rate performance and kinetic performance of lithium-ion batteries.

Polyaniline (PANI) is a conductive polymer with readily available raw materials, simple synthesis method, high conductivity and good environmental stability. The conductivity of pure PANI can reach 1.6S/cm.

Polyvinylpyrrolidone (PVP) has excellent solubility properties and is soluble in common solvents such as water, methanol, ethanol, NMP, DMF and DMSO. It also has good biocompatibility, high molecular surface activity, film-forming properties and micelle protection ability. It has strong hydrogen bonding and adhesion between molecules, which has a significant effect on improving the solubility of PVP-PANI binder and the adhesion and stability to silicon-based negative electrodes. At the same time, PVP has a very high viscosity, and the prepared PVP-PANI binder can be used as a binder alone without the addition of a thickener.

The inventors of this application have found that aniline can be grafted and copolymerized on the main chain of polyvinyl pyrrolidone by a nucleophilic reaction with the carbonyl group in polyvinyl pyrrolidone, and a PVP-PANI copolymer with polyaniline as the main component is obtained. In this copolymer, PVP can ensure the mechanical strength of the binder, and has a significant improvement effect on suppressing the expansion of the electrode sheet, thereby improving the battery cell cycle; PANI grafted on PVP has electronic conductivity, reduces the volume impedance effect of the binder on the electrode, and improves the rate capability of the battery cell; when preparing and using copolymers with different monomer ratios, it is found that the expansion and rate performance cannot be taken into account when used as a binder; for this reason, carbon nanotube materials are introduced for compounding, and the polar groups contained in PVP-PANI are connected to the oxygen-containing groups on the surface of the carbon nanotubes through hydrogen bonds. Compared with traditional carbon nanotubes as conductive agents, PVP-PANI is added to the electrode as a binder at the same time. Carbon nanotubes as conductive agents tend to be adsorbed on the particle surface of electrode active materials, which has little effect on the binder with great bulk resistance. By chemically compounding with conductive copolymers, it can not only improve the dispersion and distribution of carbon nanotubes in the electrode, but also help to improve the mechanical strength of the binder, and improve the cycle performance, rate performance and kinetic performance of lithium-ion batteries.

To achieve the above purpose, the technical solution adopted by the present invention is as follows:

A carbon nanotube-enhanced conductive polymer composite binder, the composite binder comprising a copolymer of polyvinyl pyrrolidone and aniline (PVP-PANI) and carbon nanotubes;

Wherein, the structure of the copolymer of polyvinyl pyrrolidone and aniline includes the following repeating units:

Wherein, n is an integer between 1 and 1000, m is an integer between 1 and 500,

A is x is an integer between 1 and 500.

Exemplarily, the structural formula of the copolymer of polyvinyl pyrrolidone and aniline includes the following repeating units:

Wherein, n is an integer between 1 and 1000, m is an integer between 1 and 500,

A is x is an integer between 1 and 500.

Exemplarily, the structural formula of the copolymer of polyvinyl pyrrolidone and aniline includes the following repeating units:

Wherein, n is an integer between 1 and 1000, m is an integer between 1 and 500,

A is x is an integer between 1 and 500.

According to the present invention, the mass proportion of the polyaniline group in the copolymer is 10% to 90%, preferably 30% to 70%; by controlling the mass proportion of the polyaniline group to be below 90%, the water solubility and bonding strength of the binder can be guaranteed, and by controlling it to be above 10%, it can be ensured that the binder has good electronic conductivity.

According to the present invention, the molecular weight of the polyvinyl pyrrolidone raw material for preparing the copolymer of polyvinyl pyrrolidone and aniline is 1000-3000000, preferably 10000-100000. By controlling the molecular weight of PVP within the above range, it can be ensured that the prepared adhesive has good bonding strength.

According to the present invention, the carbon nanotubes account for 0.5wt%-20wt% of the total mass of the composite adhesive, preferably 1wt%-10wt%; by controlling the mass proportion of carbon nanotubes to below 20wt%, the copolymerization force of the adhesive can be guaranteed, and by controlling it to above 0.5wt%, it can be ensured that the adhesive has good cohesion and electronic conductivity.

According to the present invention, the carbon nanotubes are multi-walled carbon nanotubes, the diameter of the multi-walled carbon nanotubes is 10-100nm, the length is 1-100μm, preferably the diameter of the multi-walled carbon nanotubes is 10-40nm, and the length is preferably 10-50μm. The carbon nanotubes can be selected from carbon nanotube products known in the art, for example, selected from the carbon nanotube dispersion with the brand LB217 sold by Zhuhai Guanyu Battery Co., Ltd., with a solid content of 0.1wt%-5wt%, preferably a solid content of 0.5wt%-2wt%.

The present invention also provides a method for preparing the carbon nanotube-enhanced conductive polymer composite binder, the method comprising:

(1) mixing polyvinyl pyrrolidone and aniline monomers, initiating a polymerization reaction under the action of an initiator, and preparing a copolymer of polyvinyl pyrrolidone and aniline;

(2) Mixing the prepared copolymer of polyvinyl pyrrolidone and aniline with carbon nanotubes under mechanical stirring to react and obtain a carbon nanotube-enhanced conductive polymer composite binder.

According to the present invention, in step (1), specifically:

The polyvinyl pyrrolidone is dissolved in a reaction medium, and aniline monomer is added, stirred, and polymerization is initiated under the action of an initiator. The copolymer of polyvinyl pyrrolidone and aniline is obtained after filtering and washing.

According to the present invention, in step (1), the molar ratio of polyvinyl pyrrolidone to aniline monomer is 2:0.5-8, for example, 2:1-4.

According to the present invention, in step (1), the polymerization reaction is carried out at a temperature of -20°C to 50°C, preferably at a temperature of -10°C to 30°C. Too low a reaction temperature will affect the reaction efficiency, while too high a reaction temperature will be detrimental to obtaining a PANI-PVP polymer with a regular structure and a high molecular weight.

According to the present invention, in step (1), the polymerization time of the polymerization reaction is 4 to 24 hours.

According to the present invention, in step (1), the reaction medium is at least one of hydrochloric acid and anhydrous acetic acid, preferably anhydrous acetic acid.

According to the present invention, in step (1), the initiator is at least one of ammonium persulfate, potassium persulfate, sodium persulfate, potassium dichromate and ferric chloride; the mass ratio of the initiator to the aniline monomer is 1:0.5-2, preferably 1:0.75-1.5. By controlling the initiator within the above range, the polymerization of the aniline monomer can be ensured, and the generated polyaniline molecules have a higher degree of conjugated delocalization.

According to the present invention, in step (2), the polar groups contained in PVP-PANI are connected to the oxygen-containing groups on the surface of the carbon nanotubes through hydrogen bonds.

The present invention also provides the application of the carbon nanotube-enhanced conductive polymer composite binder for use in a silicon-based negative electrode of a lithium-ion battery.

The beneficial effects of the present invention are:

(1) The present invention can improve the cycle stability of silicon-based negative electrodes and improve the first coulomb efficiency of silicon-based negative electrodes. Through the nucleophilic reaction of aniline on polyvinyl pyrrolidone, a PANI-PVP binder with conductivity is polymerized. The good bonding and toughness of PVP in the binder reduce the volume expansion effect of the active material and improve the stability of the electrode; the good electronic conductivity of PANI bridges the cracks generated during the cycle, ensuring the electrical contact of the electrodes, reducing the capacity loss of the silicon-based negative electrode during the cycle, and improving the cycle performance. At the same time, when compounded with carbon nanotubes, the carbon nanotubes not only act as a conductive additive to improve electronic conductivity, but also further act as a reinforcing agent to greatly improve the mechanical properties and bonding strength of the binder.

(2) The present invention can improve the rate and low-temperature performance of the battery. The binder of the present invention contains a large number of carbonyl and lactam polar groups, and has good affinity for carbonate electrolytes. In addition, PANI and carbon nanotubes have good electronic conductivity, and there is no need to add carboxymethyl cellulose or other binders or thickeners. The kinetic performance of the battery cell can be significantly improved, and the rate and low-temperature performance of the battery cell can be greatly improved.

Detailed ways

The preparation method of the present invention will be described in further detail below in conjunction with specific examples. It should be understood that the following examples are only exemplary illustrations and explanations of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are included in the scope that the present invention is intended to protect.

Unless otherwise specified, the experimental methods used in the following examples are all conventional methods; the reagents, materials, etc. used in the following examples, unless otherwise specified, can be obtained from commercial channels.

The degree of polymerization of polyvinyl pyrrolidone used in the following examples is 600, that is, m+n=600.

Embodiment 1:

Aniline was distilled under reduced pressure twice, and the colorless and transparent fraction at 120℃/0.01MPa was retained for use. Accurately weigh 11.1g of polyvinyl pyrrolidone (PVP) (the molar number of the structural unit is 0.1mol), and ultrasonically vibrated for 5-10min to completely dissolve it in 300ml of anhydrous acetic acid. Weigh 4.6g (0.05mol) of aniline and dissolve it in anhydrous acetic acid solution of PVP, and stir it magnetically at 25℃ for 8h. Measure a certain volume of 2mol/L hydrochloric acid solution so that the molar ratio of hydrochloric acid to aniline is 2:1. Weigh an appropriate amount of APS and dissolve it in the hydrochloric acid solution. Place the prepared APS hydrochloric acid solution in a separatory funnel and slowly add it dropwise to the acetic acid solution of aniline (the dropping time is about 50-60min), and initiate aniline polymerization at 5℃, and the polymerization reaction time is 12h. After the reaction is completed, the mixed solution is filtered to obtain a dark green solution. Sodium chloride and acetone were added to the solution, and a large amount of dark green precipitate was produced in the solution, and the solution became turbid. After the dark green turbid solution was allowed to stand at 0°C for 6 hours, the supernatant was removed, and the dark green precipitate was vacuum dried at 40°C for 8 hours. The dried precipitate was dissolved in 600 ml of anhydrous ethanol, ultrasonically vibrated for 10 minutes to dissolve the precipitate and filter out the residual sodium chloride in the solution, and the filtrate was retained for use. Acetone was added to the filtrate to produce a block precipitate, and after standing at 0°C for 8 hours, the supernatant was removed and the dark green precipitate was retained for use. The obtained dark green block precipitate was placed in a Soxhlet extractor and extracted with acetone and ether for 2 hours respectively. The block material after extraction was vacuum dried at 40°C for 8 hours and then ground to obtain a dark green powdery PVP-PANI polymer. 10 g of the prepared PVP-PANI polymer powder was weighed and mixed with 10 g of carbon nanotube dispersion (solid content 1 wt%), and stirred using a mechanical stirrer to obtain a carbon nanotube-reinforced composite material, which was recorded as B1.

Silicon-based negative electrode sheets were prepared using conventional processes: negative electrode active material (SiO/Graphite): B1 binder was added to water at a mass ratio of 95:5, mixed evenly and coated on the negative electrode collector (copper foil), dried at 80°C and rolled with a roller press, then cut, slit, vacuum dried, and welded to make negative electrode sheets.

The positive electrode sheet was prepared by conventional process: the positive electrode active material (lithium cobalt oxide, NCM ternary, lithium iron phosphate), conductive agent (super-p), and binder (PVDF) were added to N-methylpyrrolidone in a mass ratio of 97:2:1, mixed evenly and coated on the positive electrode collector (aluminum foil), dried at 90°C, rolled with a roller press, cut into pieces, slit, vacuum dried, and welded with the electrode ears to make the positive electrode sheet.

The electrolyte was prepared by conventional process: ethylene carbonate (EC), propylene carbonate (PC) and ethyl methyl carbonate (EMC) were uniformly mixed in a volume ratio of 1:1:1, and then LiF6P was added thereto to prepare a 1 mol/L electrolyte, and 2% of the electrolyte mass of vinylene carbonate (VC) and 5% of fluoroethylene carbonate were added as additives to prepare the final electrolyte.

The positive electrode sheet, negative electrode sheet and separator (12μm polyethylene porous bare film) are conventionally wound into a bare battery cell, placed in an aluminum-plastic film with holes punched after hot pressing, and vacuum dried for 24 hours after pre-packaging; after testing that the moisture content of the positive electrode sheet, negative electrode sheet and separator is below 200PPM, the electrolyte is injected, and then vacuum packaged to obtain a lithium-ion battery.

The rolling, cutting, slitting, vacuum drying and welding of electrode lugs used in the present invention are all conventional operations in the art.

Embodiment 2:

Aniline was distilled under reduced pressure twice, and the colorless and transparent fraction at 120℃/0.01MPa was retained for standby use. Accurately weigh 11.1g of polyvinyl pyrrolidone (the molar number of the structural unit is 0.1mol), ultrasonically vibrate for 5-10min, and completely dissolve it in 300ml of anhydrous acetic acid. Weigh 9.3g (0.1mol) of aniline and dissolve it in anhydrous acetic acid solution of PVP, and stir magnetically at 25℃ for 8h. Measure a certain volume of 2mol/L hydrochloric acid solution so that the molar ratio of hydrochloric acid to aniline is 2:1. Weigh an appropriate amount of APS and dissolve it in the hydrochloric acid solution. Place the prepared APS hydrochloric acid solution in a separatory funnel and slowly add it dropwise to the acetic acid solution of aniline (the dropping time is about 50-60min), and initiate aniline polymerization at 5℃, and the polymerization reaction time is 12h. After the reaction is completed, the mixed solution is filtered to obtain a dark green solution. Sodium chloride and acetone were added to the solution, and a large amount of dark green precipitate was produced in the solution, and the solution became turbid. After the dark green turbid solution was allowed to stand at 0°C for 6 hours, the supernatant was removed, and the dark green precipitate was vacuum dried at 40°C for 8 hours. The dried precipitate was dissolved in 600 ml of anhydrous ethanol, ultrasonically vibrated for 10 minutes to dissolve the precipitate and filter out the residual sodium chloride in the solution, and the filtrate was retained for use. Acetone was added to the filtrate to produce a block precipitate, and after standing at 0°C for 8 hours, the supernatant was removed and the dark green precipitate was retained for use. The obtained dark green block precipitate was placed in a Soxhlet extractor and extracted with acetone and ether for 2 hours respectively. The block material after extraction was vacuum dried at 40°C for 8 hours and then ground to obtain a dark green powdery PVP-PANI polymer. 10 g of the prepared PVP-PANI polymer powder was weighed and mixed with 10 g of carbon nanotube dispersion (solid content 1 wt%), and stirred using a mechanical stirrer to obtain a carbon nanotube-reinforced composite material, which was recorded as B2.

The difference between this embodiment and embodiment 1 in the manufacture of the battery is that the silicon negative electrode uses B2 binder to make the slurry.

Embodiment 3:

Aniline was distilled under reduced pressure twice, and the colorless and transparent fraction at 120℃/0.01MPa was retained for standby use. Accurately weigh 11.1g of polyvinyl pyrrolidone (the molar number of the structural unit is 0.1mol), ultrasonically vibrate for 5-10min, and completely dissolve it in 30ml of anhydrous acetic acid. Weigh 18.6g (0.2mol) of aniline and dissolve it in anhydrous acetic acid solution of PVP, and stir magnetically at 25℃ for 8h. Measure a certain volume of 2mol/L hydrochloric acid solution so that the molar ratio of hydrochloric acid to aniline is 2:1. Weigh an appropriate amount of APS and dissolve it in the hydrochloric acid solution. Place the prepared APS hydrochloric acid solution in a separatory funnel and slowly add it dropwise to the acetic acid solution of aniline (the dropping time is about 50-60min), and initiate aniline polymerization at 5℃, and the polymerization reaction time is 12h. After the reaction is completed, the mixed solution is filtered to obtain a dark green solution. Sodium chloride and acetone were added to the solution, and a large amount of dark green precipitate was produced in the solution, and the solution became turbid. After the dark green turbid solution was allowed to stand at 0°C for 6 hours, the supernatant was removed, and the dark green precipitate was vacuum dried at 40°C for 8 hours. The dried precipitate was dissolved in 600 ml of anhydrous ethanol, ultrasonically vibrated for 10 minutes to dissolve the precipitate and filter out the residual sodium chloride in the solution, and the filtrate was retained for use. Acetone was added to the filtrate to produce a block precipitate, and after standing at 0°C for 8 hours, the supernatant was removed and the dark green precipitate was retained for use. The obtained dark green block precipitate was placed in a Soxhlet extractor and extracted with acetone and ether for 2 hours respectively. The block material after extraction was vacuum dried at 40°C for 8 hours and then ground to obtain a dark green powdery PVP-PANI polymer. 10 g of the prepared PVP-PANI polymer powder was weighed and mixed with 10 g of carbon nanotube dispersion (solid content 1 wt%), and stirred using a mechanical stirrer to obtain a carbon nanotube-reinforced composite material, which was recorded as B3.

The difference between this embodiment and embodiment 1 in the manufacture of the battery is that the silicon negative electrode uses B3 binder to make the slurry.

Embodiment 4:

Aniline was distilled under reduced pressure twice, and the colorless and transparent fraction at 120℃/0.01MPa was retained for standby use. Accurately weigh 11.1g of polyvinyl pyrrolidone (the molar number of the structural unit is 0.1mol), and ultrasonically vibrated for 5-10min to completely dissolve it in 300ml of anhydrous acetic acid. Weigh 4.6g (0.05mol) of aniline and dissolve it in anhydrous acetic acid solution of PVP, and stir it magnetically at 25℃ for 8h. Measure a certain volume of 2mol/L hydrochloric acid solution so that the molar ratio of hydrochloric acid to aniline is 2:1. Weigh an appropriate amount of APS and dissolve it in the hydrochloric acid solution. Place the prepared APS hydrochloric acid solution in a separatory funnel and slowly add it dropwise to the acetic acid solution of aniline (the dropping time is about 50-60min), and initiate aniline polymerization at 5℃, and the polymerization reaction time is 12h. After the reaction is completed, the mixed solution is filtered to obtain a dark green solution. Sodium chloride and acetone were added to the solution, and a large amount of dark green precipitate was produced in the solution, and the solution became turbid. After the dark green turbid solution was allowed to stand at 0°C for 6 hours, the supernatant was removed, and the dark green precipitate was vacuum dried at 40°C for 8 hours. The dried precipitate was dissolved in 600 ml of anhydrous ethanol, ultrasonically vibrated for 10 minutes to dissolve the precipitate and filter out the residual sodium chloride in the solution, and the filtrate was retained for use. Acetone was added to the filtrate to produce a block precipitate, and after standing at 0°C for 8 hours, the supernatant was removed and the dark green precipitate was retained for use. The obtained dark green block precipitate was placed in a Soxhlet extractor and extracted with acetone and ether for 2 hours respectively. The block material after extraction was vacuum dried at 40°C for 8 hours and then ground to obtain a dark green powdery PVP-PANI polymer. 10 g of the prepared PVP-PANI polymer powder was weighed and mixed with 20 g of carbon nanotube dispersion (solid content 1 wt%), and stirred using a mechanical stirrer to obtain a carbon nanotube-reinforced composite material, which was recorded as B4.

The difference between this embodiment and embodiment 1 in the manufacture of the battery is that the silicon negative electrode uses B4 binder to make the slurry.

Comparative Example 1:

The difference between this comparative example and Example 1 is that the negative electrode binder uses modified styrene-butadiene rubber SBR and sodium carboxymethyl cellulose CMC known to those skilled in the art, and the electrode is made of negative electrode active material (SiO/Graphite): SBR: CMC at a mass ratio of 95:2.5:2.5.

Comparative Example 2:

The difference between this comparative example and Example 1 in the preparation of the battery is that the silicon negative electrode uses the PVP-PANI polymer prepared in Example 1 as a binder to prepare the slurry.

Comparative Example 3:

The difference between this comparative example and Example 1 in the preparation of the battery is that the silicon negative electrode uses a negative electrode active material (SiO/Graphite): the PVP-PANI polymer prepared in Example 1: carbon nanotubes (LB217) are prepared in a slurry with a mass ratio of 95:4.84:0.16.

The electronic conductivity and tensile strength of the adhesives of Examples 1-4 and Comparative Examples 1-3 were tested.

Conductivity test: The sample was ground into powder, and the powder was pressed into a disc with a diameter of 1 cm under a pressure of 20 MPa. The thickness of the disc was measured using a spiral micrometer, and the conductivity of the sample was tested using a four-probe conductivity meter.

Tensile strength test: B1-B5 adhesives were dissolved and dried (60°C vacuum) to form films, which were cut into 2.5×5.0 cm films and subjected to tensile testing using a tensile testing machine.

The peeling force of the negative electrode sheets prepared in Examples 1-4 and Comparative Examples 1-3 was tested by a 180° tensile test using a tensile machine. The batteries prepared in Examples 1-4 and Comparative Examples 1-3 were formed by hot pressing at a temperature of 80°C and a pressure of 422 kg.f, pre-charged to 4.0 V with a low current of 0.5C, and then cold pressed to obtain activated batteries. The batteries were tested for charge and discharge performance and cycle performance, and the test results are shown in the following table.

Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 PVP:PANI:CNTs 2:1:0.1 2:2:0.1 2:4:0.1 2:1:0.2 - - 2:1:0.1 Electronic conductivity S/cm 2.5× ^10-4 9.4×10 ^-4 2.8×10 ^-3 1.1×10 ^-3 - 6.5× ^10-5 3.6×10 ^-5 Diaphragm tensile strength/MPa 5.3 4.1 1.8 7.9 0.8 2.7 - Pole peeling force N/m 10.2 9.1 6.3 11.5 6.6 13.4 7.1 Battery internal resistance mΩ 25.7 23.1 19.8 20.1 35.6 28.4 29.8 -20℃ discharge ratio 71.4% 73.9% 74.1% 73.8% 47.5% 69.1% 70.6% Lithium deposition during charging at 0℃ No lithium precipitation No lithium precipitation No lithium precipitation No lithium precipitation Severe lithium deposition No lithium precipitation No lithium precipitation Expansion rate after storage at 60℃ for 30 days 7.3% 7.5% 10.2% 7.2% 8.7% 7.7% 7.6% 300T (cycle) capacity retention rate 80.1% 84.5% 76.7% 86.6% 15% 78.6% 78.8%

It can be seen from the above test results that the batteries of Examples 1-4 exhibit balanced electrical properties, and their performance in terms of battery cell internal resistance, cycle, capacity utilization at low temperature, and charging lithium deposition is significantly better than that of conventional Comparative Example 1, Comparative Example 2 without adding carbon nanotubes, and Comparative Example 3 in which PVP-PANI polymer and carbon nanotubes are simply mixed. Example 4 in which the ratio of PVP, PANI and carbon nanotubes is 2:1:0.2 has better cycle performance, lower internal resistance, and balanced performance. This is because the introduction of carbon nanotubes compensates for the decrease in conductivity caused by the reduction in PANI content, while improving the bonding strength of the composite material, ensuring the electrical contact and stability of the silicon negative electrode during the cycle. It can be seen from the above table that the conductivity of the negative electrode prepared by the carbon nanotube-enhanced PVP-PANI polymer of the present application and the tensile strength of the diaphragm are significantly improved.

The above is an explanation of the embodiments of the present invention. However, the present invention is not limited to the above embodiments. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims (13)

1. A carbon nano tube reinforced conductive polymer composite adhesive, wherein the composite adhesive comprises a copolymer of polyvinylpyrrolidone and aniline and carbon nano tubes;

Wherein the structural formula of the copolymer of polyvinylpyrrolidone and aniline comprises the following repeating units:

；

wherein n is an integer of 1-1000, m is an integer of 1-500, A is ; X is an integer between 1 and 500;

The molecular weight of the polyvinylpyrrolidone raw material for preparing the copolymer of polyvinylpyrrolidone and aniline is 1000-3000000; the carbon nano tube is a multi-wall carbon nano tube, the tube diameter of the multi-wall carbon nano tube is 10-100nm, and the length of the multi-wall carbon nano tube is 1-100 mu m.

2. The composite binder according to claim 1, wherein the mass ratio of polyaniline groups in the copolymer is 10% -90%.

3. The composite binder according to claim 2, wherein the mass ratio of polyaniline groups in the copolymer is 30% -70%.

4. The composite binder of claim 1, wherein the polyvinylpyrrolidone starting material from which the copolymer of polyvinylpyrrolidone and aniline is prepared has a molecular weight of 10000-100000.

5. The composite binder of claim 1, wherein the carbon nanotubes comprise 0.5% -20% of the total mass of the composite binder.

6. The composite binder of claim 5, wherein the carbon nanotubes comprise 1% -10% of the total mass of the composite binder.

7. The composite binder of claim 1, wherein the carbon nanotubes are multi-walled carbon nanotubes having a tube diameter of 10-40nm and a length of 10-50 μm.

8. A method of preparing the carbon nanotube-reinforced conductive polymer composite binder of any one of claims 1-7, the method comprising:

(1) Mixing polyvinylpyrrolidone and aniline monomer, initiating polymerization reaction under the action of initiator, and preparing copolymer of polyvinylpyrrolidone and aniline;

(2) And mixing the prepared copolymer of polyvinylpyrrolidone and aniline with the carbon nano tube under the action of mechanical stirring, and reacting to obtain the carbon nano tube reinforced conductive polymer composite adhesive.

9. The preparation method according to claim 8, wherein in the step (1), specifically:

Dissolving polyvinylpyrrolidone in a reaction medium, adding an aniline monomer, stirring, initiating polymerization under the action of an initiator, filtering and washing to obtain a copolymer of polyvinylpyrrolidone and aniline.

10. The method according to claim 8, wherein in the step (1), the molar ratio of polyvinylpyrrolidone to aniline monomer is 2:0.5-8;

And/or, in step (1), the polymerization is carried out at a temperature of-20 ℃ to 50 ℃;

and/or, in the step (1), the polymerization time of the polymerization reaction is 4-24 hours;

And/or in the step (1), the initiator is at least one of ammonium persulfate, potassium persulfate, sodium persulfate, potassium dichromate and ferric chloride; the mass ratio of the initiator to the aniline monomer is 1: 0.5-2.

11. The preparation method according to claim 8, wherein in the step (2), the polar group contained in the copolymer of polyvinylpyrrolidone and aniline is linked to the oxygen-containing group on the surface of the carbon nanotube by hydrogen bonding.

12. The method according to claim 9, wherein the reaction medium is at least one of hydrochloric acid and anhydrous acetic acid.

13. Use of the carbon nanotube-reinforced conductive polymer composite binder of any one of claims 1-7 in a silicon-based negative electrode of a lithium ion battery.